What is total internal reflection, principle or total internal refraction

We know that when a ray of light passes from one medium to another medium than at the separation...smartopidia

 Total internal reflection.

We know that when a ray of light passes from one medium to another medium than at the separation 

between two mediums the incident ray bends and travels into another medium. It is called refraction. Here, the refracted bends towards or away from the normal depending on the denser and rarer medium. In this case, if the incidence angle increases then refracted angle also increases; at a particular angle of incidence 

the angle of refraction becomes normal or 900. The respective angle of incidence is called the critical angle. If the angle of incidence is increased above the critical angle then there is no refraction into another medium but there is a reflection into the same medium. This phenomenon is called total internal reflection.

Consider an optical fiber consisting of a core and cladding of refractive indices n1 and n2 (here n1 > n2). Let a light ray passes from core to cladding with an angle of incidence ‘i’ and then get refracted with the angle of refraction ‘r’. The refracted ray bends away from the normal as it travels from core to cladding. If the angle of incidence increases then the angle of refraction also increases.

case (i): when I < θc then the incident ray refracts into the core.

case (ii): when i = θc, then the incident ray passes along the interface of core and cladding

case(iii): when I> θc, then the light ray will be reflected into the core i.e undergoes total internal reflection. 

According to the Snell’s law, n1 sin i = n2 sin r

 let i = θc and r = 90 then, n1 sin θc = n2 sin 90

 n1 sin θc = n2

 sin θc = n2/ n1

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